What is highway drainage?

A highway gully is a drainage pit covered by an open metal grating located on the road edge. It’s purpose is to drain rain water from the highway into the sewerage system. A highway drain is the pipe connecting the highway gully to the surface water sewer. In some circumstances the highway drain may outfall into rivers, ponds, soakaway etc. A soakaway is a drainage pit covered by a metal cover or sometimes by soil. Its purpose is to allow rain water from buildings to permeate into the surrounding subsoil. These are sometimes used to drain the highway.

A surface water sewer is a large underground drain connecting the highway drain to the sewerage treatment works. It purpose is to carry surface water, and in some circumstances surface water and foul sewerage combined, to the sewerage treatment works. The resposibility for surface water sewers is the sewerage undertaker, predominantly either www.wessexwater.co.uk or www.bristolwater.co.uk

Why do we need highway drainage?

Highway drainage systems are installed to capture surface water run-off to alleviate flooding and protect the fabric of the road.

Many open ditch drainage systems are historic and are the responsibility of the adjoining landowner for maintenance. The Highway Authority has powers to cleanse and restore the profile of these ditches as appropriate.

Highway drainage should fulfil the following objectives:

Prevent flooding, ponding and seepage, and keep the carriageway, cycleway and footway as free of standing water as possible.

Ensure surface water falling on the highway enters the drainage system or natural watercourse as speedily as possible.

How often does the Council clean highway drainage?

Highway drainage requires routine maintenance to ensure it’s continued efficiency. From time to time, additional maintenance is essential to ensure the system continues to function properly. Gullies and their immediate pipe connection are emptied and cleansed as part of an annual proactive maintenance programme.

The frequencies are:

Rural areas, once per year

Urban areas, once per year

High speed dual carriageways, twice per year

However, where persistent problems are identified with gully cleansing for example, being blocked by silt and detritus on a regular basis, the gullies are specifically identified and programmed for a greater cleansing frequency.

In some rural areas, the carriageway is drained by non-piped drains consisting of "grips" cut into the verge which feed into a ditch. Existing grips and back ditches on the whole highway network will be re-cut and cleansed on an annual basis as part of the pro-active maintenance programme.

How does the Council prioritise drainage improvements?

Enhancements may be necessary to cope with changing climatic conditions, and to remedy inadequate parts of the system.

Before any drainage system is provided a full assessment of the existing system should be made to determine whether a satisfactory solution may be obtained by thoroughly cleaning or extending the existing arrangement.

Drainage improvement schemes will be added to the structural maintenance programme and prioritised on the following basis:

Flooding of residential or commercial property.

Flooding or ponding on the highway presenting a hazard to road users.

Seepage of water or water crossing the highway on bends and gradients liable to cause aquaplaning or formation of ice.

To eliminate drainage to the highway requiring immediate works i.e. severe scouring.

Flooding of land adjacent to the highway will be considered as a separate measure on the basis of site specific evaluation.

Drainage covers, gully gratings and other ironwork that is part of the highway drainage system will be reset if they are greater than 20mm below or above the general carriageway, cycleway or footway surface where identified or notified.

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